The problem with this question is that it's a whole lot more nuanced than "Do I need it?". In short the only time you could possible benefit from one is if you use torrents, and even then it's really only public torrents. From there it depends on whether the swarm is monitored, and given how you simply can't know that it's safer to just assume that it is. But even if it is, will your ISP bother to forward the DMCA notices to you, and if they will, will they care if you take no action?

If you check enough boxes it's likely worth it "just in case", although at that point you might as well look into debrid services.